A stent is an elongated device used to support an intraluminal wall. In the case of a stenosis, a stent provides an unobstructed conduit through a body lumen in the area of the stenosis. Such a stent may also have a prosthetic graft layer of fabric or covering lining the inside and/or outside thereof. Such a covered stent is commonly referred to in the art as an intraluminal prosthesis, an endoluminal or endovascular graft (EVG), or a stent-graft. As used herein, however, the term “stent” is a shorthand reference referring to a covered or uncovered such device.
A covered stent may be used, for example, to treat a vascular aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Typically, a stent is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called “minimally invasive techniques” in which the stent, restrained in a radially compressed configuration by a sheath or catheter, is delivered by a stent delivery system or “introducer” to the site where it is required. The introducer may enter the body from an access location outside the body, such as through the patient's skin, or by a “cut down” technique in which the entry blood vessel is exposed by minor surgical means. The term “proximal” as used herein refers to portions of the stent or delivery system relatively closer to this access location, whereas the term “distal” is used to refer to portions farther from the access location.
When the introducer has been threaded into the body lumen to the stent deployment location, the introducer is manipulated to cause the stent to be ejected from the surrounding sheath or catheter in which it is restrained (or alternatively the surrounding sheath or catheter is retracted from the stent), whereupon the stent expands to a predetermined diameter at the deployment location, and the introducer is withdrawn. Stent expansion may be effected by spring elasticity, balloon expansion, or by the self-expansion of a thermally or stress-induced return of a memory material to a pre-conditioned expanded configuration.
Among the many applications for stent-grafts is that of deployment in branching lumen, and more specifically in bifurcated lumen, such as for repair of abdominal aortic aneurysms (AAA). Various stent-graft configurations are known in the art for bifurcated applications. Referring now to FIG. 1, there is shown an illustration of the typical morphology of a human aorta 10 afflicted with an abdominal aortic aneurysm 12. An abdominal aortic aneurysm 12 is typically located proximally of renal arteries 14a and 14b and distally of branching iliac arteries 16a and 16b. Arteries 16a and 16b are typically referred to as “external” iliac arteries, whereas arteries 17 are typically referred to as “internal” iliac arteries. The location of normal (not afflicted with an aneurysm) aortic walls 18 are shown with dashed lines. The portion of aorta 10 between aneurysm 12 and renal arteries 14a and 14b as shown in FIG. 1 is referred to herein as neck 20. The neck is typically a critical fixation zone for stent-grafts placed to repair abdominal aortic aneurysms. Poor fixation may allow blood flow around the stent-graft, which can put pressure on the aneurysmal wall.
A substantial percentage of patients have necks that are non-circumferential. Others may have calcification in the neck. Non-circumferential or calcified necks may impede proper fixation of the stent-graft. In some patients, the aorta is angled and may have an inflection point in the portion of the neck where the stent-graft needs to be affixed. Still other patients exhibit a neck length of 1.5 mm or less and have historically not been considered good candidates for stent-grafts because of insufficient fixation area for the distal end of the stent-graft.
Even when a stent-graft is implanted in an aorta with acceptable morphology, over time after implantation of a stent-graft, the aneurysm may become weaker, resulting in morphological changes due to shrinkage of the diseased and surrounding tissues. Changes in anatomy may cause a stent-graft to bend or even kink, and may also cause the neck portion of the stent-graft to migrate into the area of the aneurysm, which may result in the leakage of blood around the graft.
Finally, placement of AAA stent-grafts typically requires great skill and proper hospital equipment to enable the desired precision. In particular, effective viewing systems are often advantageous to enable vision of the implantation procedure. Some hospitals have better viewing equipment than others. Placement inaccuracies can result in post-procedure complications for the patient. Accordingly, it is desirable to provide good vision of the deployment area during implantation of any stent-graft.
Thus, as discussed above, there are a number of ways in which fixation of a stent-graft may be problematic. It is therefore desirable to provide a method and apparatus that overcomes or at least mitigates many of the difficulties noted above, and provides more accurate and effective fixation of stent-grafts. The need for improved fixation is not limited only to AAA stent-graft applications for difficult morphologies, but may extend to processes for implantation of any type of endoluminal device anywhere in the body, even in routine morphologies.